The effect of a short term aerobic pretreatment step on the anaerobic co-digestion of the organic fraction of municipal solid wastes : liquid extract addition versus solid phase addition

Dimitrios Komilis thanks TECNIOspring programme for the 2014-2016 incoming fellowship in UAB (no. TECSPR13-1-0006). Raquel Barrena thanks TECNIOspring programme for the outgoing + return fellowship (no. TECSPR15-1-0051). Goal of the work was to study the effect of mixing aerobically pretreated organic municipal solid wastes (OFMSW) with raw OFMSW in an anaerobic digestion process. The optimum time of aerobic pretreatment was found to be five days, as this was indicated via biological activity measurements (oxygen uptake rate, enzymatic activities, temperature). The aerobically pretreated wastes or a liquid extract from those pretreated wastes were, each separately, mixed with simulated OFMSW in various experiments. The mixtures were anaerobically digested for 28 days and five different treatments were performed including the blanks. The methane generation results were fitted to a typical anaerobic model to calculate theoretical maximum methane potential, maximum methane generation rate and theoretical lag time. Results indicated that the addition of 5-day aerobically pretreated OFMSW in solid form to raw OFMSW resulted in a 18 % net increase of the methane production. The Rmax was also increased by 39 % while no significant differences in the lag time of the methanogenic phase were observed. The addition of the liquid extract that was obtained from the 5-day pretreated OFMSW did not result in a statistically significant increase of the net methane production of the raw OFMSW.